Are those spam threads or real user created content? Because if those or real user created posts/threads and public perhaps it is a better idea to keep them and monetize them with e.g. Google ad-sense, no? I believe 1mln threads would bring a few $k/monthly whatever the subject of those threads is.
Anyway, you might find this helpful ->
https://vborg.vbsupport.ru/showthread.php?t=223716